Kris Letang, the best Pens D is making 3,5 this year, and 3,5 next year. Last year, before his injury, he was about to be the second most productive D-man in the whole NHL.

So, Subban is worthing more than Letang ?

Go to the NHL stats pages for the 2011-12 season and seen how PK is far from being in the top twenty in any categories.. except penalties (mostrly indiscipline) and giveaways for a defenseman.

Letang signed his contract in March 2010 he had 27 points that season.

If you read up on the situation a bit before talking out of thin air you'd see opinions like Dregger saying that if he was offered 3.5-4 million he thinks Subban would take it. So the number are around the same adjusting for 2 extra years of growth, both have made similar impacts in the league at time of signing, I'd maybe even say Subban a bit more. Not to mention that Subban is much more marketable then Letang so yeah if Subban is actually asking for 4 million that seems very ok to me.